Plastic container with rupturable seal

ABSTRACT

A rupturable seal includes a first and second thermoplastic polymer layer and a third continuous polymer layer between the first and second polymer layers. The third polymer layer forms a first physical polymer blend with the first layer, and forms a second physical polymer blend with the second layer. The third layer can include a continuous fibrous strip of nonwoven polymeric microfibers, which may melt within a sealing region. Methods of making such seals and multi-compartment containers comprising such seals are disclosed. Applications for food storage and preparation and other diverse end uses are disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This international application claims priority as a continuation-in-part to U.S. application Ser. No. 10/455,055, “Nonwoven Plastic Pouch Separator”, filed Jun. 5, 2003, pending, and also claims priority to U.S. Provisional Application 60/511,064, “Plastic Pouch With Rupturable Seal For Food Storage and Preparation”, filed Oct. 13, 2003.

FIELD OF THE INVENTION

The invention relates to plastic containers such as pouches that comprise at least one rupturable seal, used in many cases to divide the container into a plurality of compartments. The invention also relates to the application of such pouches in food storage and preparation, and other applications.

BACKGROUND

Containers used for the storage of materials that react together if allowed to come into contact with each other are known. Such containers can include means, for example sealed boundaries or barrier strips, and the like, to prevent contact between the reactive materials until there is a need for the reaction product. The seals and barrier strips can separate containers, particularly plastic containers or packages, into a number of separate compartments that can then isolate a variety of liquids or mobile reactive components. Disruption of a barrier between compartments provides a pathway for reactive components to intermix and react together. Reaction may be encouraged by hand manipulation of a flexible package.

The use of multi-compartment plastic packages is known for containment of reactive materials including reactive liquid monomers that require separation from activator materials that convert the liquid monomers into cured resin materials. A typical combination of reactive components comprises as a liquid epoxy monomer separated from a stable mixture of a liquid polysulfide polymer and an amine activator for the epoxy monomer. When mixed together, these materials undergo exothermic reaction to produce a heat-resistant, tough resinous product that finds use as an electrical insulating material.

U.S. Pat. No. 2,932,385 (Bollmeier et al.) discloses a multi-compartment plastic package suitable as a container that keeps a liquid epoxy monomer composition separate from a liquid polysulfide polymer. The package includes two sheets of a thermoplastic film fusion bonded together along the outer edges of the film and divided into compartments by heat-sealing a breaker strip between the films so that it extends to the fused edges of the films. A breaker strip is weaker physically than either of the films, which allows it to break, under stress, before rupture of the fused edge seals of the plastic package. U.S. Pat. No. 3,074,544 (Bollmeier et al.) describes several methods for forming multicompartment packages using a variety of sealing strips.

Other references to multi-compartment plastic packages may be found in, for example, U.S. Pat. No. 2,756,875 (Yochim), U.S. Pat. No. 2,916,197 (Detrie et al.), U.S. Pat. No. 3,809,224 (Greenwood), U.S. Pat. No. 4,961,495 (Yoshida et al.), and U.S. Pat. No. 5,287,961 (Herran). The '495 Yoshida reference discloses that the compartments can be filled with medical and pharmaceutical substances, and also mentions foods. U.S. Pat. No. 2,971,850 (Barton) discloses other materials that may be stored in multi-compartment plastic containers, and identifies a multi-compartment package including a rupturable membrane to separate the components of an enzyme system. The package preserves enzyme activity before rupture of the membrane and reaction between the enzyme and an appropriate substrate material.

A need however remains for a rupturable seal forming material to lower the cost, improve consistency, and increase the efficiency of processes used for manufacturing multi-compartment plastic storage bags and other containers having increased shelf life. Such seals should ideally be suitable for food storage and preparation applications, and various other end-use applications.

BRIEF SUMMARY

The present application discloses an exemplary rupturable strip seal, comprising micro-fibers such as melt-blown micro-fibers, that separates by application of force, causing the seal to rupture to allow admixture and/or interaction of the contents previously isolated in separate compartments of a plastic container. The rupturable seal can form a structure that temporarily isolates the contents of a container from the outside environment, or can provide a divider to seal compartments of a plastic bag or pouch or similar container from each other. A multi-compartment plastic bag or pouch provides suitable containment for two or more materials that admix and/or react on contact to yield useful products such as coating materials, encapsulant materials, bonding materials, and the like.

The exemplary rupturable seal is particularly suitable for food product applications. Different food components can be sealed in the separate compartments of a multi-compartment plastic pouch, which can then serve as a food storage article. In some cases the food-filled pouch can be frozen for long-term storage until needed. To prepare the food for consumption, the pouch can be placed in a microwave oven where the food components are heated and cooked separately from each other for a first time period as they are exposed to microwave radiation. During the first time period, vapor pressure (for example, due to steam) in at least one of the compartments gradually increases to a level that causes the rupturable seal to break, thus permitting admixture of the different food components present in the compartments adjacent the ruptured seal. The rupture of the seal marks the end of the first time period and the beginning of a second time period, during which the different food components are allowed to cook together in the pouch as microwave radiation continues to bombard the pouch. The microwave radiation is turned off at an appropriate time, marking the end of the second time period. The pouch can then be opened such as by tearing, cutting, or otherwise breaking the permanent seals around the periphery of the pouch. In some cases methods other than microwave cooking can be used to heat the pouch, such as methods that utilize solar or infrared radiation, or methods that use convection or conduction of heat such as placing the pouch in boiling water or another heated fluid. In some cases the pouch can comprise an expandable portion in which the cooked food contents can collect such that the pouch sits upright on a flat surface, permitting the user to eat the cooked food contents directly from the opened pouch.

In some food or non-food applications, for example, applications where heating is not desired, the pouch can be opened by hand manipulation such as squeezing or pulling. Still other applications may utilize a container comprising a molded plastic base and a thin plastic cover sheet sealed to portions of the plastic base to form isolated compartments therebetween.

Exemplary strip seals include substantially a single material, such as a layer of meltblown plastic micro-fibers. This differs from the description of breaker strips in U.S. Pat. No. 2,932,385 (Bollmeier et al.), which bond together two films on opposite sides of a breaker strip consisting of a central fibrous portion separating outer filmstrips. The outer filmstrips comprise the same thermoplastic polymer as the two films bonded to them on either side of a breaker strip. This produces a filmstrip-to-film seal equally as strong as the seal formed by direct fusion sealing of one film to another. The fibrous central layer provides a weakened plane of the breaker strip, which splits along its central plane when the films are jerked apart. With bursting of the breaker strip, the two filmstrips remain separately attached to different films that form the sides of a plastic package or container. According to the '385 Bollmeier et al. reference, another example of a breaker strip consists of a thin porous paper coated on both surfaces with a thin continuous layer of polyethylene, which heat seals to polyethylene films that form the outer envelope of a multi-compartment package. The paper center of the breaker strip remains porous and susceptible to leakage by premature rupture or separation due to chemical attack. Either of these conditions produces an opening between compartments. Premature rupture leads to undesirable leakage between compartments.

As indicated above, previously known seals were composite structures having a fibrous portion sandwiched between continuous layers of barrier film of substantially the same chemical composition as thermoplastic sheets of film used to form multi-compartment bag structures. Exemplary strip seals disclosed herein are uniform structures formed by cutting strips from fibrous webs such as webs composed of melt blown micro-fibers. In some embodiments, these webs can be characterized by effective fiber diameters ranging from about 2.5 μm to about 7 μm. Effective fiber diameter (EFD) is further defined below and for purposes of this application is generally close to but slightly greater than average fiber diameter. In some embodiments, the webs can comprise fibers whose actual diameters range (on average) from a fraction of a micrometer to about 10 or 20 μm. One method for micro-fiber formation uses a known process that disrupts high velocity streams of a thermoplastic polymer to produce small diameter fibers referred to herein as melt-blown micro-fibers.

Exemplary bags, pouches, or other containers can use sheets of a composite film laminate having a surface of polyethylene, or other thermoplastic heat-seal material, adjacent to a surface of polyethylene terephthalate (“PET”), or other strengthening material. These sheets are oriented or arranged such that the heat-seal material of each opposing sheet is on the interior of the pouch, and the strengthening material is on the exterior of the pouch. A rupturable strip seal, used to separate two adjacent compartments of a plastic pouch, can have fibers whose melting point is higher than that of the thermoplastic heat-seal material on the interior of the polymer sheets. In that case, where the heat seal temperature is below the melting point of the micro-fibers, bond formation between the strip seal and a thermoplastic polymer sheet relies upon the thermoplastic material melting and flowing into the interstices of the micro-fiber strip, forming physical polymer blends of the micro-fibers and each thermoplastic material to produce a bonded structure. On the other hand, where the heat seal temperature is at or above the melting point of the micro-fibers, all or a portion of the micro-fiber strip seal can melt as the molten thermoplastic polymer sheet material flows into the interstices of the micro-fiber strip, again forming a physical polymer blend. In either case, a physical polymer blend of the micro-fiber strip and the thermoplastic material on one side of the strip is produced, and a physical polymer blend of the micro-fiber strip and the thermoplastic material on the opposite side of the strip is also produced. And in either case, air that initially resides within the interstices of the micro-fiber strip is substantially displaced from or otherwise driven out of the bonding area. An exemplary embodiment of a multi-compartment pouch or other container includes a strip seal of polypropylene micro-fibers between layers of polyethylene. Polyethylene wets polypropylene micro-fibers so there is no need to laminate compatible films of polyethylene on either side of the polypropylene or alternatively to add polyethylene fibers to the strip seal.

Although it is not necessary for the micro-fiber strip to melt during sealing, a seal including thermoplastic polymer micro-fibers, when incorporated into a pouch, has sufficient burst strength, between about 0.1 kg/cm² (1.45 psi) and about 1.25 kg/cm² (17.5 psi), to prevent solid or liquid transfer across the seal representing the impermeable barrier. However, the micro-fiber strip seal can rupture under moderate hand stress without damaging the thermoplastic sheets or breaking the edge seals around the periphery of the bag.

An advantage of strip seals of melt blown polymer micro-fibers is the high uniformity of an inert material that provides barrier strip seals of greater reliability and consistency than breaker strips described previously as including a central layer of non-woven or paper material. The manufacture of such breaker strips requires a complex process including at least one additional step to laminate thermoplastic material on either side of the non-woven or paper materials before the resulting breaker strips may be bonded to thermoplastic polymer sheets during package formation. Additional processing steps increase the probability of inconsistent product performance leading to scrap and higher manufacturing costs.

A melt blown polypropylene micro-fiber web is a readily available material obtained by a one-step process that is more controllable than processes used to produce laminates of polymer films and non-woven or paper material. In addition, it is possible to manufacture single layer melt blown polymer micro-fiber webs having controlled levels of basis weight, fiber diameter, and porosity. Single-layer strip seals have no internal planar interfaces that could fail by premature rupture or separation following chemical attack, for example. In cases where the sheet materials are transparent, strip seals formed from melt blown polymer micro-fiber webs can also advantageously provide a visual indication of effective barrier seal formation when the sealed junction changes from an opaque to a substantially transparent condition. The transition from opaque to transparent provides an observable signal of formation of a barrier seal that can provide effective separation between compartments of a plastic package.

A multi-compartment plastic pouch or bag container can be fabricated to include two opposed sheets of thermoplastic polymeric film and at least one melt blown micro-fiber strip seal. Formation of fused edges, by heat-sealing around the edges of the film sheets forming the periphery of the bag produces a hermetically closed interior space or envelope. A suitably positioned strip seal, bonded between the two opposed sheets by application of heat and pressure, divides the interior space into a first and second adjacent compartment disposed on opposite sides of the strip seal, and forms a barrier to material transfer between the first and second compartments.

Moreover, the disclosed fibrous strip can provide a rupturable seal when sandwiched with heat and pressure between a first thermoplastic polymer layer having a first melting point and a second thermoplastic polymer layer having a second melting point. With adequate heat and pressure, material from the first thermoplastic polymer layer flows at least partially into one side of the fibrous strip, advancing into the interstices between individual fibers of the strip. Likewise, material from the second thermoplastic polymer layer preferably flows at least partially into the opposite side of the fibrous strip, also advancing into the interstices between individual fibers. This can occur when the melting point of the fibers within the fibrous strip is greater than that of the first and second thermoplastic polymer materials. Exemplary rupturable seals are formed when the first and second thermoplastic polymer materials contact each other through the thickness of the fibrous strip to form physical polymer blends. Depending upon bonding conditions, the portion of the fibrous strip within the sealing region may still contain individual discernable micro-fibers or may have melted. The presence of the individual fibers (or melted fibers) produces a bond or seal that is weaker than a seal directly between the first and second thermoplastic polymer layers. Thus, an applied force can cause the seal to split along the embedded fibrous strip, producing a controlled peel along the length of the rupturable seal.

In some embodiments, a first thermoplastic material that flows into a first major surface of the fibrous strip can be considered to form a first boundary layer bonded to the first polymer layer, and a second thermoplastic material that flows into a second major surface of the fibrous strip can be considered to form a second boundary layer bonded to the second polymer layer. The fibers making up a sealing interlayer have a melting point higher than the melting points of the first and second thermoplastic materials and can comprise a plurality of micro-fibers having an average effective fiber diameter from about 2.5 μm to about 7 μm. The first boundary layer includes a first portion of the plurality of micro-fibers surrounded by the first polymer material. The second boundary layer includes a second portion of the plurality of micro-fibers surrounded by the second polymer material. The rupturable seal can have a frangible interface between the first boundary layer and the second boundary layer. The rupturable seal parts at the frangible interface by application of a force causing separation of the first boundary layer from the second boundary layer.

These and other aspects of the invention will be apparent from the detailed description below. In no event, however, should the above summaries be construed as limitations on the claimed subject matter, which subject matter is defined solely by the attached claims, as may be amended during prosecution.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the specification reference is made to the appended drawings, where like reference numerals designate like elements, and wherein:

FIG. 1 is a plan view of a pouch comprising a rupturable seal prior to filling the individual compartments with suitable contents and edge sealing the pouch closed;

FIGS. 1 a, 1 b, and 1 c are fragmentary plan views in the vicinity of an edge of alternative embodiments to that of FIG. 1;

FIG. 2 is a sectional view along line 2-2 in FIG. 1;

FIG. 3 is a schematic close-up cross-sectional view of the edge of a rupturable seal;

FIG. 4 is a plan view of a pouch similar to that of FIG. 1 but incorporating an expandable portion in one of the compartments;

FIG. 5 is a plan view of multi-compartment pouch comprising multiple rupturable seals forming more than two compartments;

FIG. 6 is a plan view of a multi-component pouch comprising intersecting micro-fiber strip seals that form multiple rupturable seals in a four-compartment pouch;

FIG. 7 is a plan view of a two-compartment pouch incorporating a combination rupturable seal and permanent seal to permit an enhanced mixing feature;

FIGS. 7 a and 7 b are fragmentary plan views of alternative embodiments to that of FIG. 7;

FIG. 8 is a schematic sectional view of a container having a molded rigid plastic base and a cover sheet bonded to each other with at least one rupturable seal; and

FIG. 9 is a plan view of a single compartment pouch incorporating a disclosed rupturable seal as an opening thereof.

GLOSSARY

As used herein, the following terms shall have the meanings shown unless otherwise indicated.

“Micro-fiber” refers to fibers whose average diameter is about 20 μm or less, preferably from about 1 μm to about 10 μm.

“Effective fiber diameter” is a calculated dimension, known to one of ordinary skill in the art, derived from the pressure drop across a micro-fiber web of known thickness, polymer density, and basis weight.

“Rupturable seal”, “barrier seal”, and the like refer to an airtight closure formed using at least one plastic sheet, which closure can be opened without tearing the plastic sheet. In some cases such a seal can comprise a composite structure comprising at least two layers of thermoplastic polymer bonded to the sides of a strip seal, as well as boundary layers produced by infusion of molten thermoplastic polymer into spaces between micro-fibers forming side portions of a strip seal.

“Strip seal,” “separator strip seal,” “microfibrous strip seal,” “sealing interlayer,” “fibrous strip”, and the like refer to a collection of fibers formed into a long, thin porous layer or layers, and in some cases can comprise a blown micro-fiber web, converted into strip form for use in the formation of rupturable seals between suitable layers of polymer film or film laminates. This definition also includes strip seals (etc.) embedded between layers of thermoplastic material, where the fibers of such strip seals may have been partially or completely melted to form shapes, other than fibers, capable of producing a physical blend with another polymer.

A “boundary layer” forms on either side of a barrier seal when molten polymer infuses into a strip seal to provide, on cooling, a polymer-filled side portion of the strip seal.

“Frangible interface” refers to a central portion of a rupturable seal. In some cases the frangible interface may reside between boundary layers and may include micro-fibers substantially free of thermoplastic polymer. This provides a relatively weak interface that preferentially parts during forced separation of opposing boundary layers. In some cases the frangible interface can include portions wherein the first polymer contacts the second polymer. In some cases, depending on the bonding temperature and the dwell time under pressure, molten polymer can substantially fill the internal space of a strip seal. A major portion of a frangible interface may in some cases comprise a micro-fiber-containing gap between boundary layers.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

A multi-compartment plastic pouch or bag container, such as that shown at 10 in FIGS. 1 and 2, may be fabricated to include two opposed sheets 12, 14 of thermoplastic polymeric film and at least one melt blown micro-fiber strip seal 16 or similar fibrous strip. Depending upon the duration and pressure of bonding, layers of polyethylene (or other suitable thermoplastic) fuse together at temperatures between about 120° C. and about 200° C. to form fused, permanent heat-sealed margins 18 a, 18 b, 18 c around the edges of the film sheets, producing a hermetically closed interior space or envelope. In FIGS. 1 and 2, such a space is created after formation of a final edge seal at the top of the pouch opposite margin 18 b. A suitably positioned strip seal 16, bonded between the two film sheets 12, 14, divides the interior space into first and second adjacent compartments 20, 22 respectively, and represents a barrier to material transfer from the first to the second compartment. The bonded strip seal 16 forms a rupturable barrier seal 16 a along the strip seal and preferably has a narrower width than that of the strip seal itself, as indicated by the broken lines extending along strip seal 16 in FIG. 1. Note that the rupturable barrier seal 16 a is not preserved at those places where it overlaps a heat-sealed margin such as 18 b, thus ensuring that when a rupture occurs in the barrier seal 16 a, the peripheral edge seals remain intact and the interior space of the pouch remains closed. The sizes and positions of the two compartments depend upon the position of the strip seal inside the plastic package. It will be appreciated that additional strip seals can be positioned between the two film sheets to increase the number of compartments in a bag container.

The region of overlap (labeled 15 in FIG. 1) at the end of the strip seal 16, where a permanent edge seal such as 18 b crosses the strip seal, forms a seal that is not as weak as the central portion of barrier seal 16 a due to mechanical reinforcement by being flanked on opposed sides by permanent edge seal 18 b, but not as strong as the permanent heat-sealed margins 18 a, 18 b, 18 c due to the presence of the embedded fibrous strip or strip seal 16. Such a seal of intermediate strength at region 15 can be used advantageously as a pressure relief mechanism. Thus, for example, after closing compartments 20, 22 with a permanent top edge seal, a first amount of pressure is applied to rupture barrier seal 16 a. If further pressure is then applied (or the temperature of the pouch is increased), region 15 and its counterpart at the top of the pouch 10 provide relatively small but predictable failure points so that the pouch does not undergo a more energetic and less predictable failure through sheets 12, 14 or one of the permanent edge seals. The strength of the overlap region 15 can be adjusted by changing the sealing conditions (temperature, pressure, dwell time, and so forth) of the permanent heat-sealed margin 18 b. It can also be adjusted by selectively narrowing or widening portion(s) of the fibrous strip or strip seal 16 and then before sealing the upper and lower edge seals, aligning the narrowed or widened portion(s) with the upper and lower edges of the pouch 10. This is depicted in the fragmentary views of FIGS. 1 a and 1 b, producing modified overlap regions 15 a and 15 b respectively.

FIG. 1 c shows another fragmentary view of a portion of a lower permanent edge seal 19 formed by, for example, heat sealing film sheets such as 12, 14 described above. The edge seal may be part of any of the container embodiments described herein, or may be part of an otherwise conventional multi-compartment pouch or other container, or even an otherwise conventional single compartment pouch or container. But included in the seal is a piece of fibrous strip or strip seal 17 large enough to span the width of the edge seal and preferably, but not necessarily, extending slightly beyond the seal into the sealed compartment 21. The sealed strip is flanked on opposed sides by strong permanent seals, but is rupturable. The strip seal 17 can thus provide a simple, low cost pressure release mechanism for virtually any type of plastic container.

Suitable film materials for multi-compartment plastic packages may be selected from a group of polymer films and film composites including a suitable heat-seal layer. Formation of the barrier seals may use any of a wide range of thermoplastic polymers to provide bonding layers melting below or close to the melting point of the micro-fibrous strip seal. Suitable materials may be selected from, for example, polyolefin polymers including polyethylene and polypropylene, polyvinyl chloride, and ethylene vinyl acetate and film composites including any of these materials laminated with films of polymers that can provide additional strength, such as polyethylene terephthalate (PET), that melts at temperatures higher than those used during the bonding process. The strengthing layer such as PET preferably forms an outer layer or exterior of the pouch or other container, and is preferably composed of a material whose melting point is also higher than that of the thermoplastic material forming the interior of the pouch or container. Alternative strengthening layers can comprise or be substantially composed of, for example, polypropylene, nylon (polyamide), polyethylene naphthalate and other polyesters, fluoropolymers, and metal foils such as aluminum foil.

Manufacture of a blown micro-fiber polymer web preferably relies upon a method of the type described by Van Wente in Industrial and Engineering Chemistry Vol. 48, No. 8, 1956, p. 1342. U.S. Pat. No. 3,978,185 (Buntin et al.) describes a similar but improved method that reduces the amount of undesirable coarse “shot” or “beads” of material larger than about 0.3 mm in diameter. The manufacturing method has been shown to yield micro-fibers as fine as 0.1 μm to 1.0 μm for various thermoplastic materials including nylon (polyamide), polyolefins, polystyrene, poly(methyl methacrylate), poly(ethylene terephthalate), and polytrifluorochloroethylene. Fiber formation requires the use of an apparatus that is essentially a ram-extruder that forces molten material through a row of fine orifices and directly into two converging, high velocity streams of heated air or other appropriate gas. Air temperature and polymer-melt temperature have separate adjustment, as do the velocities of the streams of air and thermoplastic fluid materials.

A resin, ejected from an extruder nozzle at a temperature between about 290° C. (550° F.) and 430° C. (800° F.), enters a gas stream as molten strands of resin that the gas stream attenuates into fibers. Fibers form at a point that lies within the gas stream where cooling has progressed sufficiently to solidify the resin material. Since the hot-melt resin issues from the nozzle directly into the confluence of the two air streams, the greatest amount of attenuation occurs at this point of exit. Depending upon the exact temperatures and velocities used, the fibers cool to a solid form after being carried by the air stream a distance of about 2.5 cm away from the nozzle tip.

Newly formed fibers move away from the nozzle in a dispersed turbulent stream at very high velocity. With typical air conditions of about 315° C. (600° F.) and about 3.5 kg/cm² (50 psi), this velocity might equal or exceed sonic velocity, i.e. about 500 meters per second (1600 feet per second). A moving 16 mesh screen provides a surface that separates the air blast from the fibers to provide a random deposit of fibers that may be stripped from the screen as a (nonwoven) fiber mat for collection on a wind-up reel, with or without being densified using press rolls. Melt blown polymer webs, preferably polypropylene webs, suitable for fabrication of strip seals as described herein preferably have an effective fiber diameter (EFD) from about 1 to 20 μm, preferably 2.5 μm to 7 μm, more preferably 4 μm to 6 μm. Polymer webs or fibrous strips composed of a collection of micro-fibers in a nonwoven layer have been found to be useful in the disclosed applications, where the fibers have an average (actual) diameter ranging from about 4 μm in some embodiments to about 12 μm in other embodiments. An exemplary range for average fiber diameter is considered to be about 1 to 20 μm, more preferably about 4 to 6 μm.

Preferably, in its original condition before sealing, the strip seal or fibrous strip is both (1) continuous and (2) porous. By this we mean that the strip is (1) substantially devoid of through-openings, yet is also (2) porous by virtue of interconnected interstitial spaces between the fibers. The continuous feature prevents or discourages softened thermoplastic sheet material from flowing in direct paths across the strip, which would form islands of uninterrupted thermoplastic material and detract from the desired rupturable nature of the seal. The porous feature however permits softened thermoplastic sheet material to form serpentine or tortuous paths into at least the outer portions of the strip seal, and if the micro-fibers of the strip do not melt during sealing, then preferably across the thickness of the strip. After sealing, the portion of the strip seal or fibrous strip that extends out of the sealing area generally remains continuous and porous, because it was not subjected to the full heat and pressure in the sealing area. The portion of the strip within the sealing zone generally remains continuous, and forms physical polymer blends (i.e., interconnecting material structures) with the adjacent thermoplastic layers whether or not the micro-fibers remain intact or melt during the sealing process.

Preferred combinations of micro-fibers and thermoplastic sheet materials are those that do not adhere well to each other when placed in molten contact with one another. This is to avoid the formation of an excessively strong seal bond if the bonding conditions cause both the thermoplastic sheet material and the micro-fibers in the fibrous strip to melt. Preferred combinations of micro-fiber/thermoplastic materials include but are not limited to: polypropylene/polyethylene, nylon/polyethylene, PET/polyethylene, fluoropolymer/polyethylene, fluoropolymer/polypropylene, nylon/polypropylene, and PET/polypropylene, where the first material in each combination refers to the composition of the micro-fibers, and the second material refers to the composition of the thermoplastic material layer that bonds to the fibrous strip.

A convenient package for separately storing reactive materials, particularly fluid materials, as well as food components, comprises at least two sheets of thermoplastic polymeric film edge-bonded to each other along their peripheries. As used herein, “two sheets” and the like can refer to a single sheet folded over upon itself. Separation of the two components is achieved by one or more rupturable seals, also referred to herein as a strip seal that form barriers to movement of materials between the isolated compartments within the package. The material of a strip seal (i.e., the individual fibers making up the strip seal) typically has a melting point close to or higher than the interior thermoplastic film layers used to form the package. Controlled heating of thermoplastic film layers against the strip seals disclosed herein causes the film layers to at least initially melt and flow into the sides of the micro-fiber strip seal at temperatures higher than the melting point of the thermoplastic film layers but close to or lower than the melting point of the micro-fiber seal material. The micro-fiber strip seals may or may not themselves then melt depending on the sealing conditions. Upon cooling, the thermoplastic film layers bond to the micro-fiber strip seal to provide a rupturable seal.

The rupturable seal formed by bonding plastic film to a micro-fiber strip seal, as described above, has sufficient strength to completely separate material of one compartment from material in an adjacent compartment of a pouch, envelope, or other container during normal handling, shipping, and storing operations. The disclosed multi-compartment plastic pouches can maintain the required seal, in a two-part container, or multiple seals in a bag having more than two compartments, until there is a need to intermix the separated materials. In some cases, it may be appropriate to initiate the mixing process by gripping a portion of film on opposed sides of a strip seal and jerking the films in opposite directions, which ruptures the seal and allows material migration through the open seal. Complete mixing of materials can then be done by hand manipulation of the flexible plastic package. In other cases, it may be appropriate to apply pressure by squeezing one or more compartments to rupture the seal. Alternatively, vapor pressure generated inside one or both adjacent compartments, such as upon heating by microwave radiation or other suitable energy form, can be used to break the rupturable seal without the need to even touch the package. Fluid flow together with bubbling action such as is present during cooking may then suffice to adequately mix the materials after the seal between the compartments is ruptured. From the description of the sequence of actions for mixing the separated materials inside a bag container, it should be apparent that the (permanent) edge seals between the sheets of thermoplastic film are stronger than the rupturable seal.

The formation of a heat seal between portions of thermoplastic film sheets and a strip seal involves a series of process steps including inserting a strip of micro-fiber web between two sheets of film. This produces a sandwich construction having a narrow strip of micro-fibers extending between two sheets of film, each sheet having a width greater than that of the strip of micro-fibers, so that the edges of the sheets overlap the edges of the strip of seal-forming micro-fibers. Film sheets may be bonded to the micro-fiber strip following positioning of the sandwich construction between a pair of heated platens. One or both platens can include individually controlled, heated rails aligned with the strip seal, and can also if desired include heated rails along parallel edges and across the width of the sheet sandwich. The rails can be made of metal for good thermal conductivity, and can also include an outer layer or covering of a heat stable cushioning material such as a fluoropolymer or silicone rubber for a more uniform distribution of applied pressure within the desired sealing area or zone. The positioning and number of heated rails depends upon the particular design of a multi-compartment packaging container or pouch. After closing the heated platens around the sheet construction, application of pressure causes the film layers to bond to the strip seal and to fuse together along the edges and across the width of the sheets. The platen press produces a bag or pouch sealed along its parallel edges and along its base, and having at least one barrier seal separating a number of compartments. A multi-compartment bag, as described above, has an opening to each compartment for addition of the materials for which the temporary separation is desired. In FIG. 1, the openings for compartments 20, 22 are shown at 24, 26, respectively. After placing the materials in their respective compartments, the open ends of the multi-compartment package may be sealed using a second platen press that includes a heated rail to form a final edge seal. The temperature for edge seal formation may be high enough to produce a fused junction at the intersection between the edge seal and the strip seal. Formation of fused junctions of this type provides an advantage compared to previously known breaker seals including paper tissue. A junction including a paper strip may introduce a point of failure at temperatures that cause paper charring.

One embodiment uses a platen press temperature typically in a range from about 140° C. to about 150° C. This temperature range is above the melting points of the thermoplastic heat seal layers in contact with the strip seal, but below the melting point of the melt blown micro-fiber strip seal itself. The heating time is typically from two seconds to four seconds depending upon the pressure applied to the plates of the platen press. Suitable application of heat and pressure causes melting of the thermoplastic layer and migration of molten polymer into the interstices of the micro-fibers to produce boundary layers, on both sides of the seal strip, containing molten polymer that solidifies as it cools. Thermoplastic polymer flowing from one side of a strip seal may make contact with polymer flowing from the opposite side. Effective bonding between a strip seal and package films can leave at least an internal portion of the strip seal free from thermoplastic polymer to provide a frangible interface at which the rupturable seal strip parts during application of force to the plastic package causing separation of the boundary layers of the strip seal.

A preferred embodiment uses top and bottom actively heated metal rails associated with the rupturable bond, the rails having no cushioning heat stable material thereon, and heated to a temperature in the range from about 270-310° F. This temperature range is sufficient to quickly melt the thermoplastic heat seal layers in contact with the strip seal. The heating time, when both the top and bottom elements are heated, is typically from 0.5 to 2 seconds. A suitable application of pressure causes melting of the thermoplastic layers and migration of the molten polymer into the interstices of the sealing interlayer to initially occur. As the sealing cycle continues, the molten thermoplastics penetrate through the fibrous strip or strip seal, contacting each other within the strip seal. In another case, the molten thermoplastics may penetrate through the strip seal and cause the individual micro-fibers thereof to melt, resulting in a completely melted physical polymer blend, which forms the rupturable seal. In both of the above cases the rupturable seal contains polymer material (including polymer material from the inner thermoplastic sheet layers and from the micro-fibers) throughout the entire thickness and is substantially free from air in the heat sealed region. This process may be done in a batch mode to form a single rupturable seal, or it may be done in a step and repeat process forming a continuous rupturable seal for use in a continuous container making process.

An alternate process for forming a heat seal between portions of thermoplastic film sheets and a strip seal involves a series of steps of a continuous process including inserting a strip of melt blown micro-fiber web between two sheets of film. This produces a sandwich construction having a narrow strip of micro-fibers extending between two sheets of film each having a width greater than the strip of micro-fibers, so that the edges of the sheets overlap the edges of the strip of seal-forming micro-fibers. The film sheets bond to the micro-fiber strip during movement of the sandwich construction between rollers aligned along the strip seal and heated to an elevated temperature. The duration of contact of the thermoplastic film sheets with the heated rollers causes melting of the thermoplastic layer and migration of molten polymer into the interstices of the micro-fibers at least enough to produce boundary layers, on either side of the strip seal, containing molten polymer that solidifies as it cools. The thermoplastic boundary layers preferably contact each other, and the micro-fiber layers may or may not melt in whole or in part in the area of the seal.

Alternative means for heating the sealing region of the disclosed rupturable seal (or permanent seals) include the use of ultrasonic horns, induction heating, and radio frequency heating.

The continuous sandwich construction formed as described above may enter another heat sealing device that produces peripheral seals by application of heat and pressure along the edges of the overlapping sheets and across the sheet structure as needed to provide plastic packages having two compartments separated by a strip seal as shown, for example, in FIGS. 1 and 2. One edge of each compartment remains open for charging of reactive materials, food materials, or other desired materials to be temporarily isolated, after which a heat sealer forms the final fused edge seal that closes the compartments and isolates the materials from each other until the rupturable seal is broken.

In the process of forming the rupturable seals and containers with these seals, individual portions of the seal area may be contacted multiple times by the heated sealing bars. Heating may occur from one or both sides or may also be done in a manner in which alternate sides of the seal are heated in separate contact steps such as in a step and repeat process similar to that previously described. In some cases, the formation of the container, the filling of the container, and the final sealing of the container can be done in one continuous process, this process commonly known as form, fill, seal.

Melt blown micro-fiber webs used for forming the preferred strip seals include non-woven, fibrous polymeric materials, preferably a polypropylene homopolymer such as #3960 or the like, having a melt flow rate from about 280-420 g/10 minutes at 230° C. (available from Atofina, Houston, Tex.). Micro-fiber webs typically have basis weights ranging from about 10 grams per square meter (gsm) to about 30 gsm, preferably about 25 gsm when using opposed sheet materials whose thermoplastic heat seal (interior) layers each have a thickness of about 3.5 mils. The ideal basis weight for a given application will depend on the thickness of the thermoplastic polymer materials forming the interior layers of the container, with smaller basis weights being more suitable for thinner thermoplastic layers, and vice versa. Preferred effective fiber diameters and actual fiber diameters are as mentioned previously. Such strip seals introduce less of a bump between packaging films and other seals, e.g. edge seals. A strip seal between about 1 cm and 1.25 cm wide, having a basis weight of 15 gsm, has a thickness of about 100 μm before sealing, and a thickness of about 25 μm (0.001 inch) after sealing.

The preferred nonwoven micro-fiber web material can become compressed, typically by a factor of two or more, in the area of the seal. This is depicted schematically in FIG. 3, where opposed heat seal rails 40, 42 press against sheets 44, 46 and strip seal or fibrous strip 48 (depicted schematically for ease of illustration) in a sealing region 50 to form a rupturable seal as described elsewhere in this application. The sheets 44, 46 each preferably comprise an inner thermoplastic layer 44 b, 46 b respectively, and an outer strengthening layer 44 a, 46 a respectively. When the heat seal rails apply heat and pressure to the construction, the fibrous strip 48, which is preferably a nonwoven arrangement of micro-fibers, becomes compressed within the sealing region 50. Molten thermoplastic polymer from inner layers 44 b, 46 b migrates into the fibrous strip from opposite sides, and if the temperatures are low enough that strip 48 does not melt, the thermoplastic materials form surface layers within the strip that preferably contact each other as shown. Strip 48 is preferably oversized with respect to the sealing region 50 so that a distal portion 48 a of the strip extends away from the fracturable seal and into a defined compartment 52. This oversizing or extension of the fibrous strip beyond the sealing region advantageously allows for normal manufacturing tolerances in the positioning of the fibrous strip relative to the heat seal rails. The distal portion 48 a of the strip is not in intimate contact with the thermoplastic layers 44 b, 46 b, unlike the central portion of strip 48 within the sealing region 50. Whether or not fibrous strip 48 melts within the sealing region 50 during sealing, the observed thickness t2 of the (melted or intact) fibrous strip within the sealing region is typically substantially less than the observed thickness of the distal portion 48 a, with relative thickness ratios of about 2 to 4 being typical.

Where at least one (and preferably both) of sheets 44, 46 is substantially transparent so that contents within the compartment(s) can be viewed by the user, strip seals formed from polymer micro-fiber nonwoven webs can also advantageously provide a visual indication of effective barrier seal formation when the sealed junction changes from an opaque to a substantially transparent condition. Fibrous strips or strip seals tend to have an opaque, typically white appearance prior to sealing. This appearance is due in large part to the highly scattering nature of the multitude of reflective surfaces formed by the individual micro-fibers when surrounded by air. This appearance changes to substantially transparent when the fibrous strip forms a successful fracturable seal to a transparent sheet because the thermoplastic material of the sheet substantially displaces the air in the sealing region so that the fibers (or melted fiber shapes) of the fibrous strip are now surrounded by the thermoplastic. Since the thermoplastic typically has a refractive index much closer to that of the micro-fibers, reflection at the micro-fiber surfaces is greatly reduced, light scattering by the fibrous strip is reduced, and light can more easily pass through the sealing region 50 characterized by the micro-fiber/thermoplastic material physical polymer blend. A consequence of this is the closer in refractive index the micro-fibers are to the thermoplastic material, the more transparent the sealing region 50 becomes. The transition from opaque to transparent provides an observable signal of formation of a rupturable seal that can provide effective separation between compartments of a plastic package. The sealing operation changes the appearance of the construction from a completely opaque (typically white) strip to a substantially clear central region (corresponding to region 50 in FIG. 3 and to barrier seal 16 a in FIG. 1) bordered by at least one and usually two opaque regions (corresponding to distal end 48 a in FIG. 3 and to the portion of strip 16 outside of seal 16 a in FIG. 1).

The porosity of a melt blown micro-fiber web depends upon basis weight and fiber diameter. These characteristics control the rate of flow of molten polymer into the interstices between micro-fibers, during the process of bonding packaging film sheets to either side of a micro-fiber strip seal. After successful formation of heat sealed container bags, the strength of a rupturable barrier seal may be evaluated using a pressurized bag-bursting machine. The test includes inflating the adjacent compartments on opposite sides of a strip seal to an air pressure at which the melt blown micro-fiber seal bursts. A preferred range of seal strength is from about 0.21 kg/cm² (3 psi) to about 0.63 kg/cm² (9 psi).

The strength of the individual rupturable seal may also be evaluated by conventional peel tests such as those described in ASTM F 88-00 (Standard Test Method for Seal Strength of Flexible Barrier Materials) or variations of this test. These test methods are particularly useful when only the rupturable seal itself is available for testing and not an entire pouch or container.

Package-forming polymer sheets suitable for use in forming the disclosed bags and pouches include polymer films having a lower melting point than the polymer used to form a melt blown micro-fiber web. As a preferred example, a multi-compartment bag uses a film laminate identified by the trade name SCOTCHPAK 29905 (also known as SCOTCHPAK ES241) available from 3M Company, St. Paul, Minn. The film laminate consists essentially of an 86 μm (3.4 mil) thick layer of linear, low density polyethylene adjacent to a 14 μm (0.56 mil) thick layer of biaxially oriented polyethylene terephthalate. Opposed sheets of the SCOTCHPAK 29905 film are positioned during formation of a multi-compartment pouch so that the polyethylene layer of both sheets is the inner layer that bonds to a strip seal during heating between about 120° C. and about 200° C. to form the barrier seal.

Various fluid components may be enclosed in the separate compartments of a multi-compartment package. For non-food applications, a typical combination of reactive components comprises as a first material a liquid polyol resin and as a second material an isocyanate crosslinking agent. These materials react to form a polyurethane encapsulating or blocking compound. A second combination of reactive components comprises a liquid having anhydride functionality and a suitable crosslinking agent. These two components react to provide a polyester encapsulant material. Component materials that react to form an epoxy resin may also be stored in multi-compartment packages. In this case the package separates a liquid, epoxy-functional, composition from a mixture of a liquid polymer and amine activator prior to formation of the epoxy resin. Activation of the reaction between resin-forming components involves gripping the outer packaging films close to the central area of one of the compartments and jerking the films apart along the axis of the rupturable seal. This breaks the strip seal by fiber separation in the frangible interface between the boundary layers of the strip seal without damaging the permanent fused edge seals of the package. Rupture of the frangible interface permits the reactive contents of the package to combine. Homogeneous mixing may require hand manipulation of the packaging envelope to promote the resin-forming reaction. Removal of a corner of the package provides an opening for release of the reacting mixture that may be dispensed into a waiting mold or other cavity or container wherein the reaction continues to completion. As an alternative to removing a corner from a multi-compartment package, a nozzle closure may be built into one of the film sheets used to produce the package.

Further non-food applications of the disclosed multi-compartment packages include use as flexible container bags for materials that react together to produce resins for a variety of end uses including resins for application in telecommunications systems, particularly as encapsulant materials. Chemical resistance testing of a melt blown micro-fiber strip seal with different encapsulating resin systems showed no damage to the seal during oven-aging at an elevated temperature of 65.5° C. (150° F.) with the multi-compartment package supporting a weight of 1 kg.

As mentioned above, the preferred rupturable seal disclosed herein is also particularly suitable for food product applications. Different food components can be sealed in the separate compartments of a multi-compartment plastic pouch, which can then serve as a food storage article. In such cases, the material selection of the strip seal and sheet materials can be conveniently selected from among the many polymer materials known to be acceptable in conventional food packaging applications. In some cases the food-filled pouch can be frozen for long-term storage until needed. To prepare the food for consumption, the pouch can be placed in a microwave oven where the food components are heated and cooked separately from each other for a first time period as they are exposed to microwave radiation. During the first time period, vapor pressure (for example, due to steam) in at least one of the compartments gradually increases to a level that causes the rupturable seal to break, thus permitting admixture of the different food components present in the compartments adjacent the ruptured seal. The rupture of the seal marks the end of the first time period and the beginning of a second time period, during which the different food components are allowed to cook together in the pouch as microwave radiation continues to bombard the pouch. The microwave radiation is turned off at an appropriate time, marking the end of the second time period. The pouch can then be opened such as by tearing, cutting, or otherwise breaking the permanent seals around the periphery of the pouch. In some cases methods other than microwave cooking can be used to heat the pouch, such as methods that utilize solar or infrared radiation, or methods that use convection or conduction of heat such as placing the pouch in boiling water or another heated fluid. In some cases the pouch can comprise an expandable portion in which the cooked food contents can collect such that the pouch sits upright on a flat surface, permitting the user to eat the cooked food contents directly from the opened pouch.

In particular, FIG. 4 shows a pouch 30 which is similar to pouch 10 except that it includes an expandable gusseted portion. For simplicity of description, elements that correspond substantially in structure and function to elements in FIGS. 1-2 are given the same reference number with the addition of a prime symbol. Pouch 30 is shown prior to charging the compartments 20′, 22′ with the food or other contents, and prior to the final edge seal operation that closes off openings 24′, 26′. Unlike pouch 10 of FIG. 1 which uses substantially flat sheets, pouch 30 incorporates folds 32, 34 in one or both opposed sheets 12′, 14′ at one of the compartments 22′. The folds permit the compartment 22′ to expand to receive a substantial portion of the combined contents of compartments 20′ and 22′, thus forming a stable base at one end of the pouch when the pouch is full. To maintain a good seal, the strip seal 16′, and therefore also the barrier seal 16 a′, preferably do not intersect the folds.

In FIG. 5, a multi-compartment pouch 60 is shown in plan view. Pouch 60 includes a plurality of fibrous strips arranged to form a plurality of isolated compartments in a single pouch. Two film sheets 62, 64 are joined together via a network of rupturable seals 66 a, 68 a, 70 a, 72 a (formed along fibrous strips 66, 68, 70, 72 respectively) and permanent seals 74 a-d formed by heat sealing or other conventional means. These seals form isolated compartments 76, 78, 80, 82, 84, pairs of which can be fluidly joined together by rupturing a selected rupturable seal as will be understood by inspection of the drawing. Filling of the compartments with the desired contents can be done before completing one or more of the permanent seals, by direct injection into the compartments after the pouch formation, or a combination thereof. Regions of overlap 86 a-h are formed as shown and can function as pressure relief mechanisms. Note that fibrous strips 66, 68, 70, 72 may or may not be of identical construction. If not, strips of different basis weight, fiber diameter, and so forth can be selected to provide rupturable seals with a desired set of predetermined seal strengths. An optional injection or dispenser nozzle, dip tube, or other device shown generically at 88 is provided for compartment 78, but similar devices can be provided for the other compartments. Alternatively, compartment 78 can in some embodiments remain empty of any contents, but can serve as a final dispensing chamber or outlet by breaking seal 68 a only after breaking the other rupturable seals and thoroughly mixing the previously separated contents of compartments 76, 80, 82, and 84.

In FIG. 6, another multi-compartment pouch 90 is shown in plan view. Pouch 90 is similar in many respects to pouch 60, but in pouch 90 two fibrous strips are arranged to cross over each other. Two film sheets 92, 94 are joined together via a network of intersecting rupturable seals 96 a, 98 a (formed along fibrous strips 96, 98 respectively) and permanent seals 100 a-d formed by heat sealing or other conventional means. These seals form isolated compartments 102, 104, 106, 108, pairs of which can be fluidly joined together by rupturing a selected rupturable seal. Filling of the compartments can be done as described above. Regions of overlap 110 a-d are formed as shown.

FIG. 7 shows a plan view of a multi-compartment pouch 120 that includes a series combination of two rupturable seals and one permanent seal separating two compartments to provide a unique mixing capability. In pouch 120, opposed thermoplastic sheets are joined together via a network of rupturable seals 122 a, 124 a (formed along fibrous strips 122, 124 respectively), permanent seals 124 a-d along the periphery of the pouch, and permanent seal 124 e connecting the rupturable seals, thus forming compartments 126, 128. Fluid communication between the compartments can be established by selectively breaking one of the rupturable seals (e.g., upper seal 122 a, such as by exerting stabilizing pressure with one's hand on the lower seal 124 a while squeezing one of the compartments with the other hand), then breaking the other rupturable seal (e.g. lower seal 124 a, such as by exerting stabilizing pressure with one's hand on the upper seal 122 a while squeezing one of the compartments). A net circular flow of combined fluid material can then be established between the chambers by alternatively pinching off or otherwise substantially closing one of the opened rupturable seals and then the other.

The embodiment of FIG. 7 requires placement and alignment of two separate, relatively short fibrous strips. In alternative embodiments, a single longer fibrous strip can be used as shown in FIGS. 7 a and 7 b. In FIG. 7 a, fibrous strip 140 has a central narrowed portion 140 a. For forming the seals between the compartments, a straight heat seal bar whose (uniform) width is intermediate that of the end portions of strip 140 and central portion 140 a is used. In this way, the fibrous strip is oversized relative to the sealing region (vertical dashed lines) at the ends, forming rupturable seals. But in the central region of portion 140 a, the fibrous strip is undersized relative to the sealing region so that a permanent seal is formed by direct contact of thermoplastic sheet materials of the upper and lower sheets on at least one side of the strip portion 140 a. In FIG. 7 b, fibrous strip 144 is uniform in width, but a heat seal bar of nonuniform width is used to produce a nonuniform sealing region 146, again resulting in a central permanent seal connected to rupturable seals on both ends of the permanent seal.

In FIG. 8, a multi-compartment container 150 is shown in schematic sectional view. Container 150 is similar to the other disclosed embodiments, except that a relatively rigid molded plastic base 152 is provided rather than a more compliant flexible plastic sheet. A cover sheet 154 is bonded selectively to base 152 with seals 156 a, 156 b, 156 c, any one or all of which can be rupturable seals formed with the disclosed fibrous strips.

In FIG. 9, a single compartment pouch 160 is shown in plan view. A rupturable seal 162 a is provided along one edge, and permanent seals 164 a-c are provided along the other edges. Fibrous strip 162, as in previously described embodiments, is oversized in width so that a portion of the strip extends beyond the sealing region corresponding to 162 a. Rupturable seal 162 a provides a convenient opener so that contents of compartment 166 can be accessed by a user.

Applications

Containers that incorporate the disclosed rupturable seals can be used in a wide variety of end-use applications. Reactive chemicals and food storage and preparation have already been mentioned. The food applications can include not only frozen foods to be heated in a microwave oven or otherwise, but also shelf-stable foods and refrigerated foods. Food applications are also intended to encompass beverage products. Other two- or three-part reactive systems are also contemplated, covering such categories as adhesives, coatings, and fillers.

Other applications are available in the medical field. For example, a multi-compartment pouch can be designed such that when a rupturable seal is broken, two or more components are mixed together that will harden in a short period of time. Before hardening, the pouch can be wrapped around a body part to create support for an injured limb, for example, and then hardening into a cast to provide support and protection. In a related example, a similar but smaller multi-compartment pouch can be designed such that after the components are mixed but before hardening, the pouch is placed into the user's ear taking the shape as it hardens to be used for hearing aide custom fit development. In another medical application, specific amounts of medications can be mixed and delivered in multi-compartment pouch to deliver desired concentrations of medicine. In some cases such a pouch can incorporate a hang tab and be used as an intravenous (IV) delivery bag.

An application useful in the dental field is a mixing pad replacement. By having pre-weighed amounts of reagents used for cavity filling, a multi-compartment pouch can be utilized to allow mixing within the pouch after the rupturable seal has been opened. When fully mixed, the pouch can be opened and used for the intended application. Another application useful in the dental field is for making impressions. A multi-compartment pouch can hold the reagents used to make dental impressions or the like. This would eliminate the need for weighing reagents, since convenient individual packages can be made.

Still other applications are in the field of indicators. In these applications, the multi-compartment pouch can provide the user with information on what conditions the pouch has been exposed to, such as temperature or pressure. Rupture indicators made in this way can inform the user of shock or temperature extremes. The pouches can also be used as seam breakage indicators.

In the area of cosmetics, one useful application is for hair coloring. The multi-compartment pouch can allow the components, such as a developer and a color crème, to be held separate until the time of use. The components can be mixed with ease within the pouch compared to the current method of adding the color crème component, contained in a tube, to the developer bottle and then shaking the open bottle with a finger over the hole. The disclosed multi-compartment pouches can also avoid the risk of handling the color crème component alone, which can be a skin and eye irritant. The pouch in such case can incorporate a spout for easy application to hair. Facial mud is another useful cosmetic application. A multi-compartment pouch can hold mud components, such as a liquid (milk or water), clay, and a powder separate until the rupturable seals are broken and the product can then be mixed and applied.

Still other applications of the disclosed containers with rupturable seals include such things as: food or medicine mixes, two-part hot or cold packs, analytical testing (resealable), perishable two-component test mixtures, single use hand towel with soap or disinfectant, single use dental whitening packs, two-part cleaning compounds for dental or other applications, complete salad components, baking components compartmentalized, wilderness food packaging, meat/marinade combinations, meat/liquid flavorant/noodle combinations, sauces mixed after ingredients are heated, two-part juice pouches, endothemic chemical for cooling, pasta and sauce, rice/chicken/vegetable combinations, heated cleaning solution into cleaning cloth, carpet or spot cleaner with peroxide on one side, customized cosmetics in two or more parts, special effects personal care such as fizzing shampoos, peroxide/colorant hair color, customizable hand lotions/fragrances, kaleidoscopes, instructional toys utilizing color, self-contained chemistry experiment kits, two-part slime toys such as Borax / white glue combinations, chemical coolers and heaters, flotation devices, light sources, automotive body fillers, curable paint systems, dissolvable bag holding curing agent, custom pigment delivery, putty and body filler, self-inflating seats, oxygen-generating components made with oxygen-permeable sheet materials for live well fish, packaging foam, packaging material such as where an acid and base combination produces a gas, two-part foaming system, rupture indicator such as for shock, temperature, and pressure, seam breakage indicator, and microwave bag vent.

Compartment Design Features

The containers disclosed herein can incorporate a wide variety of design features. For example, a pump spray device can be incorporated into a multi-compartment pouch. In this case, a dip tube and spray atomizer can be inserted into one of the compartments to allow dispensing of a combined mixture. The dip tube can extend to the bottom of one compartment so that when the rupturable seal is opened, the two separated components can be mixed becoming homogeneous and surrounding the dip tube. The solution can then be dispensed using a spray atomizer pump similar to hair spray dispensing but using a multi-component pouch.

Disclosed pouches or containers can likewise incorporate an atomizer/venturi nozzle to dispense the mixed contents of a pouch. A dip tube extends to the bottom of the pouch where an atomizer/venture device is sealed around the applicator. Pressurized air is connected to the nozzle, creating a siphoning of the pouch contents through the atomizer allowing a uniform application of the contents onto the chosen substrate.

Disclosed pouches or containers can incorporate pull handles or tabs to assist with opening. For instance, two pull handles can be secured on opposed sides of the pouch on or near the rupturable seal. By pulling in opposing directions, the seal can be readily opened to enable the separate contents to mix. The handles or tabs can comprise heat sealable polyethylene film tabs bonded directly to the outside of the pouch with a higher bond strength than that of the rupturable seal itself.

Disclosed pouches or containers can include conventional pressure relief valves. If the pouch contents are heated and release steam, the pouch will begin to inflate. If pressure within the pouch reaches a setpoint of the conventional relief valve, the valve opens to permit steam to escape the pouch to maintain pressure within a normal range to prevent the pouch from bursting. Such a relief valve can be in addition to the weakened overlap regions discussed above.

Experimental

A two-compartment bag, formed by heat sealing a strip seal of melt blown polypropylene web down the center of a polyethylene bag may be tested using either ASTM-F88-00 or ASTM-F2054-00 to determine the strength of the resulting barrier seal. The first of these tests (ASTM-F88-00) measures seal strength of flexible barrier bags. Burst strength measurement uses internal pressurization within restraining plates as described by the second test method (ASTM-F2054-00).

A. Comparison of Blown Micro-Fiber (BMF) Barrier and Effective Fiber Diameter (EFD)

For this comparison, the bag dimensions were: width of 19.7 cm, length of 11.4 cm. Bags including a lengthwise barrier strip were manufactured on a Klockner-Ferromatik Bag Maker, Model LA III. The process included platen press activation using a temperature between about 135° C. and about 150° C., a dwell time setting between about two seconds to about four seconds and a machine pressure setting of 1.54-1.97 kg/cm² (22-28 psi). Bags of Examples 1-12 were burst using an ARO 2600 pressurized air burst machine with a flow rate setting of 9.0. Examples 1-6 of Table 1 show that at a fixed temperature the barrier burst strength increases with effective fiber diameter increase. TABLE 1 Burst Strength of BMF Webs Strip Seals of Examples 1-6 Example 1 2 3 4 5 6 Sealing 135 135 135 140.5 140.5 140.5 temperature ° C. EFD (microns) 4.7 4.5 4.0 4.7 4.5 4.0 Basis weight 25 25 25 25 25 25 (g/m²) Barrier burst 0.22 0.12 0.10 0.45 0.30 0.22 strength (kg/cm²)

TABLE 2 Burst Strength of BMF Webs Seals of Examples 7-12 Example 7 8 9 10 11 12 Sealing 140 140 146 146 146 146 temperature ° C. EFD (microns) 6-8 6-8 4.7 4.5 4.4 4.0 Basis weight 20 30 25 25 25 25 (g/m²) Barrier burst 0.74 0.50 0.49 0.44 0.41 0.34 strength (kg/cm²)

Examples 7-12 of Table 2 show that at a fixed temperature the barrier burst strength increases with effective fiber diameter increase and also with lowering of basis weight. Comparison between the results of Table 1 and Table 2 indicate that barrier burst strength increases as the sealing temperature increases.

B. Blown Micro-Fiber (BMF) Barrier Basis Weight Comparison

For this comparison (Examples 13-23), the bag dimensions were: width of 25.4 cm, length of 26.7 cm. Bags were manufactured on a Klockner-Ferromatik Bag Maker, Model LA III. The process included platen press activation using a dwell time setting about two seconds to about four seconds. The machine pressure setting was 1.54-1.97 kg/cm² (22-28 psi). During bag manufacture feeding of the strip seal web between film sheets could optionally be machine fed, using a barrier strip unwinder, or hand fed. The bags were burst using an ARO 2600 pressurized air burst machine.

Table 3 shows at a fixed temperature that the barrier seal burst strength increases with effective fiber diameter increase and also with lowering of basis weight of the micro-fiber web. Table 4 shows that bags formed using machine fed strip seal differed in burst strength from those manufactured using a hand feeding technique. The difference may be attributed to a difference in strip seal tension during feeding. TABLE 3 Burst Strength of BMF Webs Seals of Examples 13-16 Example 13 14 15 16 Sealing temperature ° C. 140 140 140 140 Basis weight 20 30 25 30 EFD (μm) 6-8 6-8 5.0 5.0 Burst strength - hand fed 1.23 1.12 0.42 0.46 (kg/cm²)

TABLE 4 Burst Strength of BMF Webs Seals of Examples 17-23 Example 17 18 19 20 21 22 23 Sealing temperature ° C. 146 146 146 146 146 146 146 Basis weight 20 25 30 25 30 25 30 EFD (μm) 4.7 4.7 4.7 4.5 4.5 4.0 4.0 Burst strength - hand fed 0.5 0.29 0.23 — — — — (kg/cm²) Burst strength - machine — — — 0.45 0.40 0.52 0.51 fed (kg/cm²)

Samples in the following sections C through I were sealed and tested in the following manner.

Heat sealing description: seals of the heat seal materials were made with a Packrite (Racine, Wis.) model R robot jaw sealer with 12 inch long sealing rails. The sealer was equipped with heated top and bottom brass rails which had a sealing width of 3/16 of an inch. This device had a thermocouple feedback controlling temperature of the sealing rails and a digital control of the sealing time. Pressure was controlled by the air pressure on the clamping cylinder. Specific sealing conditions will be listed for each of the examples.

Rupturable seal testing: when peel values are reported for the rupturable seals, they were generated by using a test method similar to ASTM F 88-00, except that the peel test was performed down the length of the rupturable seal and used a rail separation rate of 5 inches/minute. Values reported for the rupturable seal strength are the average of three separately bonded samples that were peeled. Values for the control samples are a single individual peel value.

Control materials, when noted, for each of the examples refers to the listed heat seal material sealed directly to itself without the listed fibrous strip in the sealing region.

C. Effect of Sealing Temperature on Rupturable Seal Strength

Conditions Used:

-   Heat seal (thermoplastic) film−SCOTCHPAK ES241, consisting     essentially of a 0.56 mil PET strengthening layer and a 3.44 mil     LLDPE heat seal (thermoplastic) layer. -   Fibrous strip material—blown micro-fibers (BMF) of polypropylene     (PP) homopolymer substantially similar to Atofina #3960, but     including minor additives that are insignificant for purposes of the     present application. Effective fiber diameter was 4.4 microns and     basis weight was 25 grams per square meter (gsm). -   Sealing conditions—     -   Dwell time=1.0 seconds     -   Sealing Pressure=40 PSI

Sealing Temperature=(variable) TABLE 5 Effect of temperature on the peel value of the heat seal bond with the nonwoven fibrous strip inserted into the bond line. Seal Temp. Control Examples Example ° F. lb force lb force Comments 24 240 2.316 0.001 sealing region opaque 25 250 13.400 0.039 sealing region opaque 26 260 Tear 0.116 sealing region opaque 27 270 Tear 0.145 sealing region clear 28 280 Tear 0.285 sealing region clear 29 290 Tear 0.416 sealing region clear 30 300 Tear 0.481 sealing region clear 31 310 Tear 0.302 sealing region clear 32 320 Tear 0.237 sealing region clear 33 330 Tear 0.196 sealing region clear 34 340 Tear 0.148 sealing region clear 35 400 Tear 0.165 sealing region clear

In is set of data, the seal force is initially very low as the sealing temperature is not high enough to melt the thermoplastic and form a bond. “Tear” means that the seal was so strong that the sheet tore without any seal failure. This can be seen from the control sample bond value. The published melt temperature of the sealing resin is 255° F. As the temperature is increased, the seal force becomes higher as the thermoplastic material flows better upon bonding. At a temperature of 270° F. the conditions allow the seal to become clear (i.e., transparent, indicating a substantial absence of entrapped air in the fracturable seal area) as the thermoplastic polymers from each side of the seal make contact through the nonwoven fibrous strip. Seal values continue to increase until the thermoplastic material begins to flow too much at higher temperatures and the sealing region line pressure begins to force thermoplastic material out of the sealing region, forming two beads at the edge of the sealing region or bond line, reducing the peel value of the seal.

D. Effect of Sealing Dwell Time on Rupturable Seal Strength

Conditions Used:

-   Heat seal film—(same as section C) -   Fibrous strip material—(same as section C) -   Sealing conditions—     -   Dwell time—(variable)     -   Sealing Pressure=40 psi or 80 psi

Sealing Temperature=300° F. TABLE 6 Effect of sealing dwell time on rupturable seal strength, for 40 psi sealing pressure Dwell Time Peel force Example seconds lb force 36 0.5 0.1255 37 1.0 0.4805 38 2.0 0.516 39 5.0 0.5715 40 10.0 0.856

TABLE 7 Effect of sealing dwell time on rupturable seal strength, for 80 psi sealing pressure Dwell Time Peel force Example seconds lb force 41 0.5 0.401 42 1.0 0.859 43 2.0 0.7055 44 5.0 0.6995 45 10.0 0.7895

In this set of data, the seal strength (represented by peel force) at the lowest dwell times is low due to insufficient dwell time to effectively heat and melt the thermoplastic sealing layer. At longer dwell times the seal strength reaches a relatively consistent value which would allow it to function in a container application.

E. Effect of Sealing Pressure on Rupturable Seal Strength

Conditions Used:

-   Heat seal film—(same as section D) -   Fibrous strip material—(same as section D) -   Sealing conditions—     -   Dwell time=2 seconds     -   Sealing Pressure=(variable)

Sealing Temperature=300° F. TABLE 8 Effect of sealing pressure on rupturable seal strength Pressure Peel force Example psi lbs 46 20 0.4915 47 40 0.516 48 60 0.527 49 80 0.7055

Table 8 shows that seal strength increases modestly over the range of pressures shown, with all of the rupturable seal strength values being in a usable range.

F. Effect of Fibrous Strip Basis Weight on Rupturable Seal Strength

Conditions Used:

-   Heat seal film—(same as section E) -   Fibrous strip material—BMF of polypropylene homopolymer, type     Atofina #3960.     -   Actual optically measured fiber diameter of 12 microns. Stock         basis weights of 5, 15, 20, and 30 gsm. Fibrous strip materials         were stacked to achieve the effective basis weights of 10, 40,         and 60 gsm. -   Sealing conditions—     -   Dwell time=1 second     -   Sealing Pressure=40 psi

Sealing Temperature=300° F. TABLE 9 Effect of fibrous strip basis weight on rupturable seal strength Peel Basis weight force Example grams/sq meter Lbs Comments 50 5 2.7865 clear seal region 51 10 1.439 clear seal region 52 15 1.257 clear seal region 53 20 0.8445 clear seal region 54 30 0.793 clear seal region 55 40 0.057 opaque seal region 56 60 0 opaque seal region

This data shows that at a low basis weight of fibrous strip material, the peel value of the rupturable bond is too high. At higher basis weights, there is a range where the peel value falls into the usable range. As the basis weight increases even more, the ability to make a transparent seal at a 1 second dwell time is lost.

G. Effect of Different Thermoplastic Heat Sealing films on Rupturable Seal Strength

Conditions Used:

-   Heat seal film—(see table)     -   ES33—SCOTCHPAK ES33, comprising 0.56 mil PET and 3.44 mil         Primacor 3330 ethylene acrylic acid copolymer     -   ES26—SCOTCHPAKES26, comprising 3.80 mil PET and 2.0 mil Elvax         3185 ethylene vinyl acetate     -   ES241—SCOTCHPAK ES241, as described in section C     -   Nylon/PE—3 mil nylon and 2.25 LLDPE -   Fibrous strip material—(same as section E) -   Sealing conditions—     -   Dwell time=(see table)     -   Sealing Pressure=40 psi

Sealing Temperature=(see table) TABLE 10 Effect of different heat sealing films on rupturable seal strength. Temperature Dwell time Peel value Example Film ° F. seconds Control lb force 57 ES33 290 1 Tear 0.491 58 ES26 190 5 5.29 0.931 59 ES241 300 1 Tear 0.961 60 Nylon/PE 300 10 Tear 0.916

This data shows that an effective rupturable seal can be made with a variety of thermoplastic heat seal films. Depending upon the construction of the heat seal films, different sealing conditions may need to be used to get the proper rupturable seal peel value

H. Effect of Different Sealing Strip Materials on Rupturable Seal Strength

Conditions Used:

-   Heat seal film—(same as section F) -   Fibrous strip material—(various, see table) -   Sealing conditions—     -   Dwell time=1.0 second     -   Sealing Pressure=40 psi

Sealing Temperature=300° F. TABLE 11 Effect of fibrous strip materials on rupturable seal strength. Fibrous Strip Peel value Example material lb force Comments 61 Transweb-BMF Tears Polyethylene (PE) web, TM07-27-98-02 86 gsm basis weight 62 Kimberly Clark 1.155 Meltblown PP, 20 gsm basis weight, 4.7 micron EFD 63 PGI Airlaid 4104 13.234 51 gsm basis weight; each microfiber has PET core, PE sheath 64 BBA Securon 0.753 15 gsm basis weight; 3-layer SMS “SMS” construction using PP 65 HTC 3180 easy 1.340 PP stitch 66 Pellon 1.523 polyamide Wonderweb #807

Various purchased non-woven web materials were tested for their ability to make a rupturable seal with a suitable seal strength. Several were found. In Example 61 the seal is permanent due to the same polymer in the fibrous strip and the thermoplastic bonding layer. Example 63 also shows this effect with a high peel value due to the PE in the fibrous strip construction. In Example 64, the fibrous strip had a 3-layer SMS (spun-bond/melt blown/ spun bond), each layer being composed of polypropylene (PP). Other blown micro-fibers and the SMS construction gave values in a suitable peel value range.

I. Effect of Sealing Configuration on Rupturable Seal Strength

Conditions Used:

-   Heat seal film—(same as section H) -   Fibrous strip material—(same as section G) -   Sealing conditions—     -   Dwell time=(variable, see table)     -   Sealing Pressure=40 psi

Sealing Temperature=300° F. TABLE 12 Effect of sealer configurations on rupturable seal strength Dwell Peel Time Control value Example seconds lb force lb force Comments 67 1 Tear 1.111 Heated upper and lower, one layer of tape on bottom 68 1 Tear 0.205 Heated upper and lower, one layer of tape on top and bottom 69 2 Tear 0.95 Heated upper and lower, one layer of tape on top and bottom 70 2 Tear 0.971 Heated upper and lower, two layers of tape on bottom 71 1 Tear 0 Upper heat only, no tape top or bottom. Sample flipped over, 1 second on each side 72 4 Tear 0.592 Upper heat only, 3 layers of tape on bottom. Sample flipped over, 4 second on each side

In Table 12, a “layer of tape” refers to a layer of 3M 60 PTFE film (a 2 mil PTFE tape) used to cover the sealing rails. The data in Table 12 shows that various heating rail configurations can be used to produce a rupturable seal with reasonable peel values. This includes heating the seal from one or both sides and having one or both sealing rails covered with a tape layer.

Food Examples

In these examples, different combinations of food components were charged into the adjacent compartments of two-compartment plastic pouches. The pouches were constructed using film laminate sheets similar to the SCOTCHPAK 29905 sheets described above, but where the layer of linear, low density polyethylene was composed of Dowlex 2035 LLDPE from Dow Chemical Co. Prior to charging the compartments with food, the pouches were substantially of the design depicted in FIGS. 1 and 2. A strip seal composed of a melt blown polypropylene web, slit to about 12 mm in width, was also used. The pouches were manufactured on a Klockner-Ferromatik Bag Maker, Model LA III. Pouch dimensions were: width of about 25.4 cm (10 inches), length of about 26.7 cm (10.5 inches) for “double serving” size and about 16.5 cm (6.5 inches) for “single serving” size. After the compartments, which were of substantially equal size, were charged with the selected food components, the open end of the pouch was edge sealed and the resulting food storage article was placed in the freezer compartment of a conventional refrigerator-freezer. Later, for testing, the completely frozen food storage article was removed from the freezer and immediately placed in a General Electric model JES1339WC001 Turntable microwave oven having a power rating of 1.53 kW, and the oven was turned on at the: “High” setting. The vapor pressure in the compartments was allowed to increase, and the time at which the rupturable seal was broken due to the internal vapor pressure was noted. In all cases, the edge seals of the pouches remained intact and the food components were allowed to cook together for a further period of time after the barrier seal was ruptured.

F1. Cheese Ravioli/Red Sauce (Single Serving)

In this example, one compartment of the pouch was charged with about 221 g of cheese-filled ravioli pasta, and the other was charged with about 119 g of tomato sauce. These components cooked separately for about 2 minutes and 27 seconds, at which time the barrier seal was observed to rupture. The contents of the pouch were then allowed to cook together for an additional 35 seconds, at which time the microwave oven was turned off. The pouch was removed from the oven and opened. The food was of good consistency and both components were hot.

F2. Noodles/Diced Chicken and Vegetables (Single Serving)

In this example, one compartment of the pouch was charged with about 119 g of frozen dough noodles, and the other was charged with about 51 g of diced, pre-cooked chicken and about 61 g of uncooked vegetables. These components cooked separately (noodles separate from the chicken and vegetables) for about 1 minute and 51 seconds, at which time the barrier seal was observed to rupture. The contents of the pouch were then allowed to cook together for an additional 33 seconds, at which time the microwave oven was turned off. The pouch was removed from the oven and opened. All components of the food were hot. The vegetables had a good crunchy (non-soggy) consistency, but the noodles were dried out and on the hard side.

F3. Noodles/Diced Chicken, Vegetables, and White Sauce (Single Serving)

In this example, one compartment of the pouch was charged with about 119 g of frozen dough noodles, and the other was charged with about 51 g of diced, pre-cooked chicken, about 61 g of uncooked vegetables, and about 109 g of white sauce. These components cooked separately (noodles separate from the chicken, vegetables, and sauce) for about 1 minute and 52 seconds, at which time the barrier seal was observed to rupture. The contents of the pouch were then allowed to cook together for an additional 10 seconds, at which time the microwave oven was turned off. The pouch was removed from the oven and opened. The food had hot and cold spots. The noodles were dried out and on the hard side.

F4. Rice/Diced Chicken and Vegetables (Double Serving)

In this example, one compartment of the pouch was charged with about 238 g of cooked rice and the other was charged with about 102 g of diced, pre-cooked chicken and about 122 g of uncooked vegetables. These components cooked separately (rice separate from the chicken and vegetables) for about 5 minutes and 13 seconds, at which time the barrier seal was observed to rupture. The contents of the pouch were then allowed to cook together for an additional time, at which time the microwave oven was turned off. The pouch was removed from the oven and opened. All components of the food was hot. The vegetables had a good crunchy (non-soggy) consistency, and the rice also had a good consistency.

F5. Rice/Diced Chicken, Vegetables, and White Sauce (Double Serving)

In this example, one compartment of the pouch was charged with about 238 g of cooked rice and the other was charged with about 102 g of diced, pre-cooked chicken, about 122 g of uncooked vegetables, and about 218 g of white sauce. These components cooked separately (rice separate from the chicken, vegetables, and white sauce) for about 6 minutes and 19 seconds, at which time the barrier seal was observed to rupture. The contents of the pouch were then allowed to cook together for an additional time, at which time the microwave oven was turned off. The pouch was removed from the oven and opened. The food had hot and cold spots.

Additional food examples were also performed. In one, cheese was placed in one compartment and nacho chips were placed in the other compartment. In another, cheese was placed in one compartment and a large soft pretzel was placed in the other compartment. In these cases the barrier seal again ruptured from the vapor pressure within the compartment(s) without rupturing the edge seals of the pouch. After cooking, all food components were well heated and the resulting food products were of good quality and taste.

Various modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not limited to the illustrative embodiments set forth herein. 

1. A rupturable seal, comprising: a first and second thermoplastic polymer layer; and a third continuous polymer layer disposed between the first and second polymer layers wherein the third continuous polymer layer is devoid of through openings and comprises a fibrous strip comprising nonwoven microfibers; wherein the first and third polymer layers form a first physical polymer blend; wherein the second and third polymer layers form a second physical polymer blend; and wherein said blends are formed by thermoplastic material melting and flowing into the interstices of the microfiber strip.
 2. (canceled)
 3. The seal of claim 1, wherein the first and second physical polymer blends define a sealing region of the rupturable seal, and wherein the third continuous polymer layer comprises a distal portion spaced away from the sealing region.
 4. A container comprising the seal of claim
 1. 5. A container according to claim 3, further comprising: a first thermoplastic sheet sealed to a second member along at least one permanent seal and at least one rupturable seal that defines a first compartment within the container; and wherein the rupturable seal is disposed between the first sheet and the second member to form the rupturable seal.
 6. The container of claim 5, wherein the second member comprises a second thermoplastic sheet.
 7. The container of claim 5, wherein the first thermoplastic sheet comprises an inner thermoplastic layer and an outer strengthening layer.
 8. The container of claim 5, wherein the container comprises a second compartment and wherein the rupturable seal separates the first and second compartment.
 9. A container according to claim 4, wherein the container holds a food product.
 10. A food storage article comprising the container of claim 8, and further comprising a first food compartment sealed in the first compartment and a second food component sealed in the second compartment.
 11. The food storage article of claim 10, wherein one of the first and second compartments comprises an expandable portion.
 12. A method of preparing food, comprising: providing the food storage article of claim 10; and heating the food storage article to an extent that vapor pressure in at least one of the first and second compartments causes the rupturable seal to break.
 13. The method of claim 12, wherein the pouch further comprises edge seals around the periphery thereof that do not break when the rupturable seal breaks.
 14. A method of making a rupturable seal, comprising: providing first and second transparent thermoplastic sheets; positioning a continuous fibrous strip comprising nonwoven micro-fibers between the first and second sheets to form a multilayer construction; and applying sufficient heat and pressure to the multilayer construction in a sealing region to form a rupturable seal that is devoid of through openings.
 15. The method of claim 14, wherein the applying step yields a rupturable seal that is transparent.
 16. The method of claim 14, wherein the fibrous strip is oversized relative to the sealing region. 